Aqueous ink of pigment type

ABSTRACT

The aqueous ink of a pigment type comprises a pigment, water, a water-soluble solvent and a sulfite, and may further comprise a dispersant. An example of the dispersant comprises a copolymer of a monomer (a) represented by general formula (A), and one or more monomers (b) selected from the group consisting of compounds represented by general formulae (B) and (C): ##STR1## wherein AO represents an oxyalkylene group having 2 to 3 carbon atoms, and n represents an integer of 110 to 300.

TECHNICAL FIELD

The present invention relates to an aqueous ink of a pigment type, andmore particularly to an aqueous ink of a pigment type capable ofaccomplishing the stability of jetting in ink jet printers andaccomplishing printing without causing clogging, and to an ink jetrecording method which uses the same.

BACKGROUND ART

For inks for printing and writing utensils, aqueous inks are used inmany cases because of the easiness of their production andhandleability. For example, due to the development and spread ofcomputers of late years, printing apparatuses are also spread andaqueous inks are used popularly for such printing apparatuses. The inkjet recording technique that is one of typical recording techniques forprinting apparatuses is a recording technique wherein ink droplets areexpelled from a very small nozzle directly onto a recording medium toallow the ink droplets to impact to the recording medium therebyobtaining images including characters. Of late years, this technique iswidely used because this technique has not only an advantage that theapparatus used is low in noise and good in operability but also anadvantage that images can be colored easily and plain paper can be usedas a recording medium. As techniques for jetting an ink, thepiezo-electric technique which uses a piezo-electric element for aprinting head and the thermal jet technique which uses a heater of aheating resistor element for a printing head are widely used forpersonal printers.

As inks used for the above-mentioned ink jet recording, inks of a dyetype and pigment type are conventionally used. However, on the one handthe inks of a dye type are poor in water resistance and lightresistance, and on the other hand the inks of a pigment type are poor instability of jetting to cause a nozzle to be clogged, which areproblems.

To solve the problem that causes a nozzle to be clogged with an ink, inthe inks used for ink jet printers, generally a water-soluble dye thatcan be dissolved in water is used. However, by using a water-solubledye, while the ink hardly clogs a nozzle, there are problems that theink is poor in water resistance and light resistance and that,particularly in the case of a thermal jet technique, the dye is oxidizedby excess heat at a printing head to cause the ink to be scorched easilyonto the printing head.

Further, for the inks of a pigment type, in order to prevent the inkfrom clogging a nozzle, there have been proposed a method wherein acombination of a dispersant and a carbon black having a pH of 7 or overis used (Japanese Patent Application Laid-Open 4-189876), a methodwherein a pigment is emulsified with a core material (Japanese PatentApplication Laid-Open 5-9421), and a method wherein a pigment andinsoluble resin particles are bonded with an organic silane couplingagent (Japanese Patent Application Laid-Open 5-65443), but they are notstill satisfactory.

Therefore, an object of the present invention is to provide an aqueousink of a pigment type capable of accomplishing the stability of jettingin ink jet printers as well as capable of accomplishing printing withoutcausing clogging and excellent in water resistance and light resistance,and an ink jet recording method which uses the same.

DISCLOSURE OF INVENTION

The present inventors have made intensive research and have found thatthe above object can be attained by using a sulfite in an aqueous ink ofa pigment type, leading to the completion of the invention.

That is, the present invention provides an aqueous ink of a pigment typecomprising a pigment, water, a water-soluble solvent and a sulfite. Theaqueous ink of a pigment type of the present invention is particularlysuitable for use as an ink for an ink jet recording.

Further, the present invention provides an ink jet recording method inwhich the aqueous ink of a pigment type of the present invention isused, the method comprising jetting to a recording medium the aqueousink of a pigment type of the present invention in a droplet form from anozzle by the action of thermal energy generated by a heater, such as aheating resistor element, in a printing head, thereby producing an imageon the recording medium.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the aqueous ink of a pigment type of the present invention will bedescribed in detail.

As the pigment which is a major component of the aqueous ink of apigment type of the present invention, any one can be used so long as itis a pigment. Examples of the pigment which can be used include carbonblack; C.I. Pigment Yellow 1, 5, 12, 14, 17, 24, 42, 53, 83, 95, 97, 98and 100; C.I. Pigment Red 1, 3, 4, 5, 17, 22, 31, 48, 49, 53, 63, 64,81:1, 88 and 101; C.I. Pigment Blue 1, 15, 16, 27, 28, 29, 56, 60 and63; and C.I. Pigment Black 1, 7 and 11, with carbon black beingparticularly preferred.

In the present invention, the term "pigment" refers to a solid in theform of fine particles that is insoluble in water, solvents, oils, andthe like, whereas the term "dye" refers to one that can dye water orsolvents when it is dissolved in water or the solvents. "Color ChemicalJiten" (first impression, issued in March, 1988, edited by CMC KK,Yukigousei Kagakukyokai), pp. 45-!.

Therefore, the pigment used in the present invention is different fromdyes.

Water and a water-soluble solvent that are also major components of theaqueous ink of a pigment type of the present invention are used assolvents. Examples of the water soluble solvents which can be usedinclude polyhydric alcohols and ethers thereof such as ethylene glycol,propylene glycol, diethylene glycol, triethylene glycol, polyethyleneglycol, glycerin, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, diethylene glycoldiethyl ether, diethylene glycol monobutyl ether, triethylene glycolmonomethyl ether, triethylene glycol monoethyl ether and propyleneglycol monomethyl ether; acetates; and nitrogen-containing compoundssuch as N-methyl-2-pyrrolidone and 1,8-di-methylimidazolidinone. Thesewater soluble solvents can be used singly or a combination of two ormore thereof. The aqueous ink of a pigment type of the present inventioncontains, as major components the pigment, water, and the water-solublesolvent, and further contains a sulfite. Examples of salts of thesulfite include metal salts such as a sodium salt and a potassium salt;an alkaline earth metal salts such as a calcium salt and a magnesiumsalt; a quaternary ammonium salt; primary, secondary and tertiaryalkylamine salts; and quaternary alkyl ammonium salts, with the sodiumsalt, the potassium salt and the quaternary ammonium salt beingparticularly preferred.

Further, in order to improve the dispersibility of the pigments,conventionally used dispersants can be added to the aqueous ink of apigment type of the present invention. Examples of the dispersantsinclude anionic surface-active agents such as higher fatty acid salts,higher alkyldicarboxylates, higher alcohol sulfate salts, higher alkylsulfonates, condensates of a higher fatty acid and an amino acid,sulfosuccinate salts, and naphthenates; cationic surface-active agentssuch as aliphatic amine salts, quaternary ammonium salts, sulfoniumsalts, and phosphonium salts; amphoteric surface-active agents such asbetaine type compounds; and nonionic surface-active agents such asesters of an aliphatic acid and a polyoxyalkylene compound, andpolyalkylene oxide condensates. These dispersants can be used singly ora combination of two or more thereof. Polymeric dispersants can be alsoused which include, for example, proteins such as gelatin and casein;natural rubbers such as gum arabic; glucoxide such as saponin; cellulosederivatives such as alkyl cellulose, carboxyalkyl cellulose andhydroxyalkyl cellulose; lignin sulfonate; natural polymers such asshellac; anionic polymers such as polyacrylate, styrene/acrylic acidcopolymer salts, vinylnaphthalene/acrylic acid copolymer salts,styrene/maleic acid copolymer salts, vinylnaphthalene/maleic acidcopolymer salts, sodium salts of β-naphthalenesulfonic acid/formaldehydecondensates, and polyphosphoric acids; and nonionic polymers such aspolyvinyl alcohol, polyvinyl pyrrolidone, and polyalkylene glycol. Thesedispersants can be used singly or a combination of two or more thereof.

In view of dispersion stability and preservation stability, thedispersant that can be particularly preferably used in the presentinvention comprises a copolymer of a monomer (a) represented by generalformula (A), and one or more monomers (b) selected from the groupconsisting of compounds represented by general formulae (B) and (C):##STR2## wherein R₁ and R₂, which may be the same or different, eachrepresent a hydrogen atom or a methyl group, m₁ represents an integer of0 to 2, AO represents an oxyalkylene group having 2 to 3 carbon atoms, nrepresents an integer of 110 to 300, and X represents a hydrogen atom oran alkyl group having 1 to 3 carbon atoms, ##STR3## wherein R₃, R₄ andR₅, which may be the same or different, each represent a hydrogen atom,a methyl group or (CH₂)m₂ COOM₂, R₆ represents a hydrogen atom or amethyl group, M₁, M₂ and Y, which may be the same or different, eachrepresent a hydrogen atom, an alkali metal, an alkaline earth metal,ammonium, an alkylammonium or a substituted alkylammonium, m₂ representsan integer of 0 to 2, with the compounds represented by general formula(B) including acid anhydrides thereof.

Herein, in general formula (A), R₁ and R₂, which may be the same ordifferent, each represent a hydrogen atom or a methyl group. Inparticular, it is preferred that both R₁ and R₂ are the same andrepresent a hydrogen atom, or alternatively that R₁ represents ahydrogen atom and R₂ represents a methyl group. Further, m₁ representsan integer of 0 to 2, preferably 0 to 1. Further, AO represents anoxyalkylene group having 2 to 3 carbon atoms, preferably an oxyethylenegroup having 2 carbon atoms. Further, n represents an integer of 110 to300, preferably an integer of 110 to 200. Further, X represents ahydrogen atom or an alkyl group having 1 to 3 carbon atoms, preferably ahydrogen atom, a methyl group or an ethyl group.

Specific examples of the preferred compounds represented by generalformula (A) include esterified compounds of a polyalkylene glycol inwhich one terminal thereof is blocked with an alkyl group, such asmethoxypolyethylene glycol, methoxypolyethylene polypropylene glycol,ethoxypolyethylene glycol, ethoxypolyethylene polypropylene glycol,propoxypolyethylene glycol, and propoxypolyethylene polypropyleneglycol, with acrylic acid, methacrylic acid or a dehydrogenated(oxidized) reaction product of a fatty acid; and adducts of ethyleneoxide or propylene oxide to acrylic acid, methacrylic acid, or adehydrogenated (oxidized) reaction product of a fatty acid. With respectto the adducts of ethylene oxide and propylene oxide, any of randomadducts, block adducts or alternating adducts can be used.

Specific examples of the preferred compounds represented by generalformula (B) include acrylic acid, methacrylic acid, crotonic acid, metalsalts thereof, and unsaturated dicarboxylic acid monomers such as maleicanhydride, maleic acid, itaconic anhydride, itaconic acid, citraconicanhydride, citraconic acid, fumaric acid, or alkaline metal salts,alkaline earth metal salts, ammonium salts, and amine salts thereof.

Specific examples of the preferred compound represented by formula (C)include allylsulfonic acid, methallylsulfonic acid, or alkaline metalsalts, alkaline earth metal salts, ammonium salts, and amine saltsthereof.

The preparation method of the copolymers is not particularly limited solong as the function of the obtained copolymer as a dispersant is notimpaired, and conventionally known preparation methods can be mentionedas examples. Specific examples include solvent polymerization methodsdescribed in Japanese Patent Application Laid-Open 59-162163, JapanesePatent Publication 2-11542, Japanese Patent Publication 2-7901, andJapanese Patent Publication 2-7897.

The copolymer is preferably has a molar ratio of the monomers themonomer (a)/the monomer (b)! of from 0.1/100 to 100/100.

Further, out of the copolymers, a copolymer of a polyalkylene glycolmonoester monomer in which preferably 110 to 300 mol, more preferably110 to 200 mol, of oxyalkylene groups having 2 carbon atoms areintroduced, and an acrylic acid monomer is particularly desirable inview of the dispersibility and dispersion stability of pigments.

Other components including conventionally known various additives suchas a mildewproofing agent and/or a chelate agent may be added to theaqueous ink of a pigment type of the present invention.

Although the formulation of the aqueous ink of a pigment type of thepresent invention is not particularly limited, generally the componentsare formulated in the following ranges on the basis of the total weightof the ink of the present invention:

    ______________________________________                                        Pigment:     1 to 20% by weight, preferably 2 to 10                                        % by weight                                                      Sulfite:     0.1 to 10% by weight, preferably 1 to 5                                       % by weight                                                      Water-       1 to 20% by weight, preferably 5 to 10%                          soluble      by weight                                                        solvent:                                                                      Dispersant:  0.3 to 30% by weight, preferably 1 to 15                                      % by weight                                                      Other        1 to 10% by weight                                               components:                                                                   Water:       40 to 97.6% by weight, preferably 75 to                                       92% by weight                                                    ______________________________________                                    

In the aqueous ink of a pigment type of the present invention, theweight ratio of the pigment to the sulfite (the pigment/the sulfite) isgenerally from 1/10 to 10/1, preferably from 1/3 to 3/1. If the weightratio is less than 1/10, the dispersibility of the pigment may beimpaired whereas when the weight ratio is over 10/1, the jetting of theink may become unstabilized.

In the aqueous ink of a pigment type of the present invention, when adispersant is used, the weight ratio of the pigment to the dispersant(the pigment/the dispersant) is generally from 1/10 to 10/1, preferablyfrom 1/5 to 5/1, more preferably from 1/3 to 3/1.

The preparation method of the aqueous ink of a pigment type of thepresent invention by mixing the above-mentioned components is notparticularly limited. The components can be mixed by using aconventionally known apparatus such as a ball mill, a sand mill, anattritor, a basket mill and a roll mill.

In the preparation of the aqueous ink of a pigment type of the presentinvention, it is preferable to remove coarse particles. For instance, anink that does not cause clogging can be obtained by subjecting the inkobtained after formulation to a centrifugal machine to remove particlespreferably of 2,000 nm or more in size, more preferably of 1,000 nm ofmore in size.

The viscosity of the thus obtained aqueous ink of a pigment type of thepresent invention is generally 1 to 10 cps, preferably 1 to 5 cps, inview of the stability of jetting.

The surface tension of the aqueous ink of a pigment type of the presentinvention is generally 25 to 30 dyn/cm, preferably 30 to 45 dyn/cm, inview of the permeability into the material to be printed.

The amount of dissolved oxygen in the aqueous ink of a pigment type ofthe present invention is generally 0.012 to 0.016 ml/ml, preferably0.012 to 0.014 ml/ml, in view of the stability of jetting.

The aqueous ink of a pigment type of the present invention is suitablefor ink jet recording, and when it is used for ink jet recording, anyprinter that employs the ink jet recording system can be used. Forexample, any of printers that employ the piezo-electric recordingtechnique that utilizes a piezo-electric element for a printing head andprinters that employ the thermal jet recording technique that utilizesthermal energy generated by a heating resistor element in the printinghead or the like can be used.

Particularly, the aqueous ink of a pigment type of the present inventionis suitably used for the thermal jet recording technique that utilizesthermal energy to jet the ink in a droplet form from a nozzle to arecording medium, and a heating resistor element is suitably used as asource of the thermal energy. Further, the aqueous ink of a pigment typeof the present invention can be used as an aqueous ink of a pigment typefor ink jet recording as mentioned above and in addition as an ink forusual writing utensils, such as fountain pens, ball-point pens, MagicMarkers, and felt-tipped pens.

In the aqueous ink of a pigment type of the present invention, theincorporation of the pigment and the sulfite, preferably the pigment,the sulfite, and the dispersant, can accomplish the stability of jettingthe ink, particularly when printing is carried out by using an ink jetprinter. Although the reason is not sufficiently clear, it can beconsidered as follows.

That is, it is assumed that the sulfite reacts with oxygen in the ink toreduce the amount of air (oxygen) dissolved in the ink to stabilize thejetting of the ink jet printer.

In particular, in the case where a dispersant, particularly the abovespecific dispersant, is used, the dispersant is adsorbed to the pigment,so that air (oxygen) adsorbed to the pigment is freed into the ink. Itis assumed that the freed air (oxygen) reacts with the sulfite to reducefurther the amount of air dissolved in the ink and therefore the jettingof the ink jet printer is further stabilized. Inter alia, in the casewhere the thermal jet recording technique is used, the generation ofbubbles required in the ink jetting is further stabilized and thereforethe jetting of the ink is further stabilized.

Thus, in the aqueous ink of a pigment type of the present invention, theuse of the sulfite, preferably the use of the sulfite and a dispersant,in particular the above-mentioned specific dispersant, exhibits,particularly when printing is carried out by using an ink jet printer,an excellent effect that cannot be obtained in the case of conventionalinks for recording.

The advantages of the present invention will now be illustrated withreference to Examples below, but of course the present invention is notlimited to them. Parenthetically, in the following Examples, all theparts represent parts by weight unless otherwise stated.

EXAMPLE 1

    ______________________________________                                        Carbon black:            15    parts                                          Condensate of naphthalenesulfonate:                                                                    3     parts                                          (Demol N manufactured by Kao                                                  Corporation)                                                                  Monoethanolamine:        1     part                                           Diethylene glycol:       5     parts                                          Ion exchanged water:     76    parts                                          ______________________________________                                    

The above components were dispersed for 4 hours by a sand mill to obtainDispersion A.

    ______________________________________                                        Dispersion A:          33    parts                                            Sodium sulfite:        2     parts                                            Diethylene glycol:     4     parts                                            Ion exchanged water:   61    parts                                            ______________________________________                                    

After the components were formulated, the formulation was processed by acentrifugal machine at 4,000 rpm for 20 min to remove coarse particlesthereby obtaining an ink. This ink was used for printing by using athermal jet printer BJ-10 Lite manufactured by Canon Inc. that employeda heater of a heating resistor element as a source of the thermalenergy, and good printed images were obtained. Further, it was foundthat these printed images were excellent in water resistance and lightresistance.

EXAMPLE 2

    ______________________________________                                        C.I. Pigment Red 81:1:   15    parts                                          Condensate of naphtahlenesulfonate:                                                                    3     parts                                          (Demol N manufactured by Kao                                                  Corporation)                                                                  Monoethanolamine:        1     part                                           Diethylene glycol:       5     parts                                          Ion exchanged water:     76    parts                                          ______________________________________                                    

The above components were dispersed for 4 hours by a sand mill to obtainDispersion B.

    ______________________________________                                        Dispersion B:          33    parts                                            Sodium sulfite:        2     parts                                            Diethylene glycol:     4     parts                                            Ion exchanged water:   61    parts                                            ______________________________________                                    

After the components were formulated, the formulation method shown inExample 1 was followed to obtain an ink. When this ink was used forprinting in the same manner as in Example 1, good printed images wereobtained. Further it was found that these printed images were excellentin water resistance and light resistance.

EXAMPLE 3

    ______________________________________                                        C.I. Pigment Blue 15:1:  15    parts                                          Copolymer of polyethylene glycol                                                                       4     parts                                          monoacrylate in which 130 mol of                                              oxyethylene groups were introduced,                                           and sodium acrylate  the molar                                                ratio of the monomers (the former                                             the latter) = 3/7!:                                                           Monoethanolamine:        1     part                                           Diethylene glycol:       6     parts                                          Ion exchanged water:     74    parts                                          ______________________________________                                    

The components were dispersed for 4 hours by a sand mill to obtainDispersion C.

    ______________________________________                                        Dispersion C:          33    parts                                            Sodium sulfite:        2     parts                                            Diethylene glycol:     6     parts                                            Ion exchanged water:   59    parts                                            ______________________________________                                    

After the components were formulated, the preparation method shown inExample 1 was followed to obtain an ink. The ink was particularlyexcellent in dispersibility and dispersion stability. When this ink wasused for printing in the same manner as in Example 1, good printedimages were obtained. Further it was found that these printed imageswere excellent in water resistance and light resistance.

Comparative Example 1

    ______________________________________                                        Dispersion A:          33    parts                                            Diethylene glycol:     4     parts                                            Ion exchanged water:   63    parts                                            ______________________________________                                    

After the components were formulated, the preparation method shown inExample 1 was followed to obtain an ink. When this ink was used forprinting in the same manner as in Example 1, the jetting was notstabilized.

Comparative Example 2

    ______________________________________                                        Food Black 2 (dye):    5     parts                                            Diethylene glycol:     5     parts                                            Monoethanolamine:      1     part                                             Sodium sulfite:        2     parts                                            Ion exchanged water:   87    parts                                            ______________________________________                                    

After the components were formulated, the preparation method shown inExample 1 was followed to obtain an ink of a dye type. When this ink wasused for printing in the same manner as in Example 1, although goodprinted images were obtained, the printed images were poor in waterresistance and light resistance.

As is apparent from the above results, the aqueous ink of a pigment typeof the present invention realizes an aqueous ink of a pigment type thatcan accomplish the stability of jetting and printing without causingclogging particularly when printing is carried out by using an ink jetprinter, and therefore the intended object is well attained. The aqueousink of a pigment type of the present invention exhibits an excellenteffect particularly when printing is carried out by using a thermal jettype ink jet printer.

INDUSTRIAL APPLICABILITY

The aqueous ink of a pigment type of the present invention is suitablyused particularly as an aqueous ink of a pigment type for ink jetrecording, accomplishes the stability of jetting in ink jet printers andprinting by ink jet printers without causing clogging, and is excellentin water resistance and light resistance. Further, the aqueous ink of apigment type of the present invention accomplishes printing withoutcausing clogging by removing coarse particles in the preparation.Further, according to the present invention, when the aqueous ink of apigment type of the present invention is used in a thermal jet method inwhich thermal energy generated by a heater such as a heating resistorelement is used, stabilized jetting can be secured even if the printingis carried out at a high drive frequency.

Further, the printed material in which the aqueous ink of a pigment typeof the present invention has been used is excellent in water resistanceand light resistance in comparison with the printed material in whichinks of a dye type have been used.

We claim:
 1. An aqueous ink, comprising:a pigment, water, awater-soluble solvent, a sulfite and a dispersant which is memberselected from the group consisting of an anionic surface-active agent, acationic surface-active agent, an amphoteric surface-active agent, anonionic surface-active agent, protein, a natural rubber, a glucoxide, acellulose derivative, a lignin, sulfonate, a natural polymer, anonioinic polymer and a copolymer of a monomer (a), represented by theformula (A), and one or more monomers (b) selected from the groupconsisting of compounds represented by formulae (B) and (C): ##STR4##wherein R₁, and R₂, which may be the same or different, each represent ahydrogen atom or a methyl group, m₁ represents an integer of 0 to 2, AOrepresents an oxyalkylene group having 2 to 3 carbon atoms, n representsan integer of 110 to 300, and X represents a hydrogen atom or an alkylgroup having 1 to 3 carbon atoms, ##STR5## wherein R₃, R₄ and R₅, whichmay be the same or different, each represent a hydrogen atom or a methylgroup or (CH₂)m₂ COOM₂, R₆ represents a hydrogen atom, a methyl group,M₁, M₂ and Y, which may be the same or different, each represent ahydrogen atom, an alkali metal, an alkaline earth metal, ammonium, analkylammonium or a substituted alkylammonium, m₂ represents an integerof 0 to 2, with the compounds represented by the general formula (B)including acid anhydrides thereof, wherein the weight ratio of pigmentto sulfite ranges from 1/10 to 10/1.
 2. The aqueous ink as claimed inclaim 1, wherein the copolymer is a copolymer of a polyalkylene glycolmonoester monomer in which 110 to 300 mol of oxyalkylene groups having 2carbon atoms are introduced, and an acrylic acid monomer.
 3. The aqueousink as claimed in claim 1, wherein said water-soluble solvent is apolyhydric alcohol.
 4. The aqueous ink as claimed in claim 1, whereinsaid pigment/sulfite ratio ranges from 1/3 to 3/1.
 5. The aqueous ink asclaimed in claim 1, wherein the weight ratio of the pigment to thedispersant ranges from 1/10 to 10/1.
 6. The aqueous ink as claimed inclaim 1, wherein said aqueous ink is a pigmented ink for ink jetrecording.
 7. The aqueous ink as claimed in claim 1, which has aviscosity within the range of 1 to 10 cps.
 8. The aqueous ink as claimedin claim 1, which has a surface tension within the range of 25 to 50dyn/cm.
 9. The aqueous ink as claimed in claim 1, which has dissolvedoxygen content within the range of 0.012 to 0.016 ml/ml.
 10. A method ofink jet recording, comprising:jetting the aqueous ink of claim 1 indroplet form from a nozzle to a recording medium by the action ofthermal energy, thereby producing an image on the recording medium. 11.The method of claim 10, wherein said thermal energy is applied by a heatgenerating resistor element.
 12. An aqueous ink for ink jet recording,consisting essentially of:1to 20% by weight of a pigment, 40 to 97.6% byweight of water, 1 to 20% by weight of water-soluble solvent, 0.1 to 10%by weight of a sulfite, 0.3 to 30% by weight of dispersant and 1 to 10%by weight of other components.